Tibial bone density may affect implant stability and functional outcomes following total knee replacement (TKR). Our aim was to characterise the bone density profile at the implant-tibia interface following TKR in mechanical versus kinematic alignment. Pre-operative computed tomography scans for 10 patients were obtained. Using surgical planning software, tibial cuts were made for TKR either neutral (mechanical) or 3 degrees varus (kinematic) alignment. Signal intensity, in Hounsfield Units (HU), was measured at 25,600 points throughout an axial slice at the implant-tibia interface and density profiles compared along defined radial axes from the centre of the tibia towards the cortices. From the tibial centre towards the lateral cortex, trabecular bone density for kinematic and mechanical TKR are similar in the inner 50% but differ significantly beyond this (p= 0.012). There were two distinct density peaks, with peak trabecular bone density being higher in kinematic TKR (p<0.001) and peak cortical bone density being higher in mechanical TKR (p<0.01). The difference in peak cortical to peak trabecular signal was 43 HU and 185 HU respectively (p<0.001). On the medial side there was no significant difference in density profile and a linear increase from centre to cortex. In the lateral proximal tibia, peak cortical and peak trabecular bone densities differ between kinematic TKR and mechanical TKR. Laterally, mechanical TKR may be more dependent upon cortical bone for support compared to kinematic TKR, where trabecular bone density is higher. This may have implications for surgical planning and implant design.

The mechanical alignment (MA) for Total Knee Arthroplasty (TKA) with neutral alignment goal has had good overall long-term outcomes. In spite of improvements in implant designs and surgical tools aiming for better accuracy and reproducibility of surgical technique, functional outcomes of MA TKA have remained insufficient. Therefore, alternative, more anatomical options restoring part (adjusted MA (aMA) and adjusted kinematic alignment (aKA) techniques) or the entire constitutional frontal deformity (unicompartment knee arthroplasty (UKA) and kinematic alignment (KA) techniques) have been developed, with promising results. The kinematic alignment for TKA is a new and attractive surgical technique enabling a patient specific treatment. The growing evidence of the kinematic alignment mid-term effectiveness, safety and potential short falls are discussed in this paper. The current review describes the rationale and the evidence behind different surgical options for knee replacement, including current concepts in alignment in TKA. We also introduce two new classification systems for “implant alignments options” and “osteoarthritic knees” that would help surgeons to select the best surgical option for each patient. This would also be valuable for comparison between techniques in future research